X-ray imaging systems of the type mentioned are becoming more widely used. Typically, one mode of operation is radiographic, in which individual images are recorded with a dose ensuring a good image quality, and are stored. Furthermore, fluoroscopy is a mode of operation in which a plurality of images are recorded in series without being stored, with the x-ray dose being lower in fluoroscopy than in radiography. Furthermore, a hybrid mode of operation between fluoroscopy and radiography is known in which the fluoroscopy image sequences are interrupted by the recording of individual images (in the radiography mode). Tomography is a further known mode of operation.
In a more recent system, the same flat-panel x-ray detector and the same x-ray radiation source are used in all modes of operation. These are usually moved together, occasionally also relative to one another, with the aid of an x-ray C-arm, for example, onto which the flat-panel x-ray detector and the x-ray radiation source are attached. A control device controls the movements and the settings of both the x-ray radiation source and also the flat-panel x-ray detector. This means that in every mode of operation the control device must fix at least one control parameter related to the functioning of the flat-panel x-ray detector and, furthermore, it must fix at least one control parameter not related to the functioning of the flat-panel x-ray detector. Presently, those modes of operation which differ in fixing the control parameter not related to the functioning of the flat-panel x-ray detector are the focus of interest. (They regularly additionally differ in the at least one control parameter related to the functioning of the flat-panel x-ray detector used.)
Flat-panel x-ray detectors usually comprise a semiconductor with a scintillator located above it. In the case of flat-panel x-ray detectors, there are inhomogeneities over the entire face of the sensor. These inhomogeneities can be created by defective pixels, nonlinearities in the amplification or different dark currents. The images recorded by the flat-panel x-ray detector should be subjected to a corrective step so that the influence of the inhomogeneities is removed. Thus, the inhomogeneities have to be acquired in some form in advance. This occurs within the scope of a calibration process. By way of example, an image can be recorded without x-ray radiation during the calibration, or image series in which the x-ray radiation intensities are variable can be recorded.
Until now, the calibration process simulated the mode of operation in detail. This means that, during the calibration process, the control parameters not related to the functioning of the flat-panel x-ray detector are regularly fixed in exactly the same manner as when operating the x-ray imaging machine with the associated mode of operation.
By way of example, the so-called x-ray technique is defined for each mode of operation. The zero-point technique, one-point technique, two-point technique and three-point technique are differentiated. In the zero-point technique, the x-ray radiation source is regulated to that dose which was previously used in the fluoroscopy mode. In the one-point technique, the dose is fixed and the system then fixes the tube voltage (in kV) and the duration of the irradiation multiplied by the current strength (in mAs) from this. In the two-point technique, the tube voltage and the mAs-value are respectively individually set as parameters. In the three-point technique, the pulse time, during which the x-ray radiation source radiates, is fixed as a parameter in addition to these two parameters.
Fluoroscopy usually uses the zero-point technique, radiography uses the one-point technique, the two-point technique or the three-point technique. In the hybrid mode, the zero-point technique or one-point technique is used. In tomography, the two-point technique is used, and, as an alternative, a type of one-point technique in which the time is given by the traverse speed and traverse angle.
Machine movement fixes another type of control parameters. In a simplified fashion, the parameter can be defined to fix whether machine movement is taking place at all. Machine movements are possible in fluoroscopy but not in radiography, and hence they are not possible in the hybrid mode either. There are machine movements in tomography.
A further control parameter fixes whether a series of images or individual images are recorded. Image series are recorded in fluoroscopy, individual images in the case of radiography, and series images and individual images are recorded in the hybrid mode. Tomography likewise records individual images.
In the prior art, the control parameters mentioned have the same settings in the calibration process as they would have otherwise. The respective x-ray technique of the mode of operation is used and machine movements take place if they also take place during the mode of operation.
Correspondingly, one or more calibration process possibilities have to be stored in the control device for each mode of operation. These calibration processes are selected by means of an input device. The programming of these multifaceted calibration processes is very complex. Once the calibration processes have been fixed, it is difficult to carry out a change.